The present invention relates to circuits for controlling clocks such as quartz electronic clocks. The circuit on which the present invention is based is derived from the need for a circuit which can generate a sequence of pulses for controlling the motor of a quartz clock which displays the time in analog manner (with hands).
The motors used in the production of these clocks can actuate a movement whenever the current flow through a winding is inverted.
FIG. 1 shows a typical connection diagram for one of these motors which uses MOS type transistors.
FIG. 2 shows the waveforms required for the correct operation in the event of the movement of the minute hands being controlled. The waveforms are given for two logic signals SN1 and SN2. As can be seen, both signals SN1 and SN2 have pulses t1 with square forms, with a high logic level ("1") and a duration of 125 ms separated by an interval t2, with a low logic level ("0") and a duration of 30 seconds. The two signals SN1 and SN2 are sent to two control terminals S1 and S2 respectively. As can be seen, the inversion of the direction of the current occurs every 60 seconds. In particular:
when S1=0 and S2=0 the winding is short-circuited and no movement is possible; PA1 when S1=1 and S2=0 a diagonal is activated, and the hand is advanced by one minute; PA1 when S1=0 and S2=1 the second diagonal is activated with the consequent inversion of the current in the winding, and it then becomes possible to advance the hand by a further minute. PA1 counting 960 clock periods for the first 30 seconds; PA1 counting 1920 clock periods for a time interval of 60 seconds from the first pulse; PA1 resetting to zero and counting to 960 and 1920 again, taking account of the fact that the two successive pulses must be directed to the other output.
The presence of the dual pulse is required in applications of an automotive nature in order to guarantee the movement of the hand in conditions of low supply voltage, typical of the starting phases of a car.
In conditions of normal operation, the second pulse does not generate any movement since there is no inversion of the current direction; conversely, the second pulse supplements the first pulse in the above low voltage conditions.
The "one touch" type resetting of the time is performed by activating a push button (not illustrated); each time the push button is pressed, which gives rise to a low logic level at a PULSE input (PULSE=0), the inversion of the current flow through the winding has to be ensured such that the hand is advanced by one minute. If the push button is activated for more than one second, the fast time resetting phase is entered, and a sequence of pulses with a period of 100 ms is enabled at the outputs.
FIG. 3 shows the wave forms relating to the time resetting phase. Assuming that the final pulse during normal operation has been sent to the output S2, the action on the push button will cause the output S1 to be activated.
In the prior art, the circuits used for solving the above-mentioned problem comprise interconnected contacts; implementation is achieved by the truth tables relating to each single function performed. Since 4 pulses of a duration of 125 ms and at 30 second intervals are to be generated from a 32 Hz clock, the following operations have to be performed:
For the time resetting phase, a counter is used with the function of checking the duration of the action on the push button and two counters which, respectively, generate the individual pulses for the "slow" resetting of the time and the sequence of pulses for the "fast" time resetting phase.
The object of the present invention is to provide a circuit which can produce the sequence of control pulses during the various operating phases, illustrated in FIGS. 2 and 3, using a single counter, thus reducing the complexity and cost of the circuit.
In accordance with the present invention, this object is achieved by a circuit having the characteristics given specifically in the following claims.
In particular, the solution according to the invention optimizes the size in terms of areas of silicon on the integrated circuit, using a single 11-bit counter both for the normal operating phase and for the one touch time resetting phase, and, further, it performs the function of controlling the duration of the action on the push button.